System



Nov. 30 1926. H. W. O'NEILL SIGNALING SYSTEM Filed OCT.. 3, 1924 /y/ FOLARIZED lill Patented Nov. 30, 1925.

insane TnlCN-Et T0 VITESTERN ELECRG CBE'EPANY, INCORPORATED, 0E' NEXV IGR-K, ll. Y., A. CREORAION OF :l-TEW YORK,

SIGNALING STEM.

appucaumi ined eetbaar This invention relates to signaling systems and more particularly to a method ot and apparatus Ytor producing and applying signaling cu 1rents to intorm a calling subscriber or operator that ringing operations are under way on a telephone connection.

As well understood in the art, current 'tor operating a signal or bell at a called telephone station is usually ot low frequency such as 16 or 20 cycles per second. In the handling ot local connections various arrangements have, in the past, been employed for automatically detlecting a suitable amount ot such low frequency current into the lineot a calling party to produce a tone usually referred to as an audible ringing signal or a ring back signal, in the receiver duri the periods such signaling current is applicc to the called line. While various desuccess have been had with such arrangements in local service work, they are not adapted to, nor adequate for, use in connecti n with toll and long distance systems. For example, on lines provided with equipment tor simultaneous telephony and telegraphy low frequency signaling current, ot

sufficient magnitude to operate the usual signals or bells employed, cannot be used due to its adverse eiect on the telegraph equipment. Further, such low frequency ring back signals are not suitable for transmission over circuits which may be relatively non-conductive or opaque to currents of suoli low frequencies. This may beclue to coils and equipment, particularly in the form of telephone repeaters which are adapted to afford a maximum transmission eiiiciency for the higher frequency currents in the voice range, but which eltectively obstruct passage of the low frequency ringing currents. The control ot call signals over such-circuits is ordinarily accomplished by the use of composite ringers, whereby the low Jfirequency ringing current controls relay equipment to connect current ot the order of 135 cycles tor transmission over the line, which in turn controls other relay equipment at the distantl or receiving end to connect the usual 16 or 2O cycle current to actuate the receiving device. y

ln local exchange systems wherein the betere mentioned audible ringing signals are employed, such signals are usually manifested in the calling subscribers receiver 1n the form ot a welldeiined tone corresponding tov,

c, ieee.

the successive halt waves oit the ringing current employed. Usually. the arrangements employed for vdeflect/ing this current towards the calling end of a connection result in nonunitormity ot the volume or intensity ol the signals in the telephone receiver, the character and length ot the called line having substantially as marked an etiect in this regard as the character and length ot the calling line. y

The character ot the audible signal eniployed as mentioned in connection with the handling ot local service trallic appears to have now become a well understood torni et signal both to telephone users and the telephone operating torce. lllieretore, a universal or common ring back signal tor all classes ot telephone service, may, therefore, be best and most readily realized by provi ding such a signal current oit a character which will be substantially unchanged regardless ot the line to which it is applied.

The principal feature oit this invention' therefore, resides in a system tor providing a ring back signal wherein means are employed for producing alternating current of a frequency suitable and adequate tor transmission over substantially form ot telephone circuit and wherein other means are employed for modulating said current by current ot a second frequency and vl'or applying such modulated current to the calling line.

Another feature oit the invention resides in providing means whereby when signaling current of one frequency is connected to one section ot a line, current ot a dir'lerent trequency varied or modulated by said first mentioned frequency is connected with another section ot' said line and whereby said sections ot the line are rendered independent ot each-other as regarcs the current respectively present therein. A

Another feature resides in a method ot producing an alternating current wav ot one frequency varied or modulated in accordance with a second frequency which consists in generating an alternating current ot a relatively low frequency and applying it to the primary side of a transformer, in periodically varying a source of direct current at a higher rate than said alternating current frequency by means ct a short-circuiting vibrator in series with said direct current source and in applying said varied gli! directcurrent to the. primary side ot. said transformer whereby said low trequencyV alternating current atiects the opera -ion of said vibrator to produce in the secondary of said transformer an alternating current Wave of the frequency of vibrator Varied in amplitude in accordance witlrthe frequency oitl said low retpiency alternating current.

Still another` feature resides in a method otproducing an alternatingy current modulated wave, which consists in generating anJ alternating current of a relatively low irequency andpassingit through the primary winding' ci a transformer andthe windings' cfa short-circuiting vibrator to cause said vibrator to operate, thus Varying the amplitudeot the alternatingv current flowing in the primary winding ofV the transformer tov pro- Vduce a modulated wave in the secondary winding thereof.

therfeatures oi the intention Vwill. :ippear trom the Jfollowing description and ajpended claims in connect-ion with the accompairying` drawings in nf'hich F igs. 1 and 2. illustrate alternate arrangements tor'practicing the features ot the invention, and Figs. 8 and l are curves illustrating' the modulated currents produced b y the'respective arrangements shown in- Figs. 1 and 2.

Referring to Fig. 1 ot the drawing, let ithe assumed that a call, originating in a" first toll area at point 15; for a station at point B in a second toll area, is routed by 'vzy of an originating' operators position at point C to an operators position which commands the link circuit D which may serve for completing,l the connection' betweenv the two remote points. The operation ot key l in the link circuit D applies ringing current over an obvious' path from a source 1. torcalling the station l5. The key K also connects the winding 5 of transformer i2 to the calling'v line extending` to point A, it being' assumed that the answering plug 10 ol the link circuit D is inserted in jack 11.

Assume that adirect current source 12 ot. approximately constant voltage be connected in series with winding' 9. stantially constant direct current will flow' in its circuitl` the magnitude ofthe current he'ifr determined by the resistance of the circuit andthe E.' M. F. of the source. if, as illustrated in Fig. 1, there be also-4 included in thefcii uit a vibrator 3 which, in short-A circuiting` itsv energizing windings Varies the resistance 'ci' the direct current'circuit, the

currentthrough winding' 9f will hecause'd to rise and tall. rlhe ditlerence between the nia-Ximuin and minimumV values `of this di-VVV rect current willdepend both upon the inagnitudeofthe resistance which is short-cin cu-it'dv and upon'the- M. F. of the source vA larger E; lli; F, will give a' larger' changein current, other conditions remaining they same and a smaller E. MpF. a

smaller change in current. It the Vibrator operates to close its armature contact 425 times per second, the unidirectional current in winding 9 will increase and decrease L.L25 times per second and in consequence there will be induced Ain winding 5, which is inductfyely related to winding 9, an E. M. F. ot Lli2 cycles frequency. This alternating current has a substantially constantmagnitudek which dependsfupon the FJ. M. F'. .of source 12. Assume further thatV current source 1 produces alternating current of twenty cycles frequency and that the inductance` 6 permits current ot this frequency to pass `through windingl l to ground. ln consequence oi the' inductive relationv beeen*v windings et and 9 ani alternating E.

duced inl winding 9;. Accordingly', the'Fi.

be apparent that when the twenty cycle E. M. F. aids source 12 thus increasing the unidirectional current through winding 9, the 425 cycle FNM. F. induced Vin winding 5 will be increased and that when the 20rcycle E. M. F. opposesthat of'source 12, the 425 cycle E. M'. F. in winding 5 will be' diminished. From another view-point the effect of the twenty cycle E.' M. F is merely' to increase or diminish the etfect.' of source 12. Since the 425cycle E. M. F. induced in winding 5 increases and decreases twenty times per second, the 425 cycle current may be saidV to be modulated at the lower frequency.

The upper curve of'Fig; 3 direct current flowing in the primary winding" 9ct' transformer 2 as Varied by the 2O cycle current. it will be observed that' when the upper halt of the 2li-cycle wave is at its maximum, the amplitude o'tthe direct cur# rent pulsations are at a; maximum and that they gradually diminish in amplitude un'- til the lower half oi the :20-cycle crave reaches its maximum.

The loirer'curve of Fig. represents ne modulated 42e-cycle alternating current wave present'in the seccmlar'yv winding 5 ot'transiormer 2 caused by' the primary uf'indings as shown in t-heupper curve., lt will be understood, therefore, that Vthe 425 cycle currentser' es asa carrier wai/*ef in transmitting the low frequency 20 cycle -current'oy r the calling circuit to'any operator "that .may he'` listening" in`l on' t ie F. oittwenty cycles frequency will he` M. F et the direct current flowing rom current in subscriber at A. This modulated current cuits.

The. inductancc 6 may, as before nien- Y tioned, be understood as forming a path of relatively high impedance to the direct current pulsations set up by vibrator 2:3. A condenser 8 serves tofavorably affect the tone quality of the output current and also overcomes any tendency relative to sparking et the contact of the vibrator.

ln the handling of toll traffic, called subscribers stations are usually reached by Way of trunlrlines extending from the toll board to the local switchboard. Such trunks may be arranged either for control on a nianual or an automatic basis. In such tems, it is common practice to provide relays Tvhich respond at the moment a connection is extended to the line called for the purpose of applying ringing current thereto Which application may be continued until automatically disconnected by the response of thecalled station. A variation of this procedure provides that a toll operator may start the ringing current which thereafter continues until discontinued, due to the response of the called subscriber.

In the arrangement of Fig. 2, a relay 21 may be considered as in association with a runk circuit as before described and controlled in a Well known manner, not shown, to connect ringing current from a source 22 to the tip and ring conductors T and It terminating in a plug 27 which may be assinned to be. inserted in the jack of a called line. .lt Will be noted that relay 21 in operating also disconnects the conductors of the trunk to the left thereby preventing the ringing current from flowing bacl over the calling end and at the same time connects the terminals of transformer Winding 2u across this portion of the trunk.

Fig. 2 differs further from the arrangement of Fig'. l in that the QO-cycle source is connected in series with a polarized vibrator @et and the primary Winding Q3 of transformer 26.

lili/lith relay 2l energized, a circuit also entends from the e-cycle source 22 through the Winding of polarized vibrator 24 and primary Winding 23 of transformer 26 to ground, thereby causing the vibrator `windings to be energized.

u Depending upon the connection of the vibrator in the circuit, its armature will be attracted against itscontacts, thereby causin?,l it to vibrate during part of one-half Wave of each cycle, but due to the opposite direction of the current during the other half Wave, the windings will he ene ized in an opposite direction to repel the. s nature away from its Contact,thereby7 causing it to remain at rest duringsuch half Wave.

Fig. 4; represents d grainniatically the character of the current flowing in the primary' and secondary windings of the transformer. rllhe upper curve representiing` the QO-cycle current in the primary as varied durino' each positive half Wave by the action or the vibrator, and the loiver cui i of the figure slioivs the n'icdulated Wave present inthe secondary of the transformer. it will be observed that due to the non-vibraof the armature of vibrator 2d during 1/2 of each of the QO-cycle periods, there will he a corresponding interruption of the t ne applied to the left-hand portion of the trunk circuit.

What is claimed is:

1. In a modulating system, a source of direc v current, a vibrator adapted to short-cir.'- cuit itself when energized and operated by said direct current and a source of alternating current superimposed on said direct current to vary the direct current energizing said vibrator in accordance With the Wave form of said alternatingl current.

2. ln a modulating system a circuit including a coupling device, a polarized selfshort-circuiting vibrator and a source of direct current for operating said vibrator at a predetermined rate, a source of alternating current and means for applying said alternating current to said vibrator to alternately increase and decrease the effective voltage of said direct current.

3. In a modulating system a transformer. a source of direct current and a source of low frequency alternating current, a short circuiting vibrator having a tuned armature therefor, said armature operating in response to said direct current for producing, in conjunction vvith said transformer, alternating current of a relatively high frequency and means for superimposing said low frequency current on said direct current to cause the amplitude of said direct current to vary in accordance with said lou1 frequency whereby said high frequency current is modulated in accordance with said lou7 frequency.

il. In a system for convert-ing direct current into alternating current, sources of direct current and low frequency alternating current, a 'vibrator of the short-circuiting type having a tuned armature responsive to said direct current for producing relatively high frequency alternating current, and means to apply said loW frequency alternatalternating current,y a transformer, sourcesof pulsating direct and low frequency alternating current included in circuit With said transformer whereby said source of pulsating current is Varied by said W frequency alternating current to produce a modulated alternating current in a secondary Winding of said transformer, a first signale ing circuit and means for connecting it WithA said low frequency current source and a second signaling circuit joined to said secondary winding of said transformer under control Vof said means.

6. lnv a signalingsystem, a source of high frequency carrier vcurrentv comprising a sourceV of direct current, a vibrator and a transformer Winding', a source of lou7 frequency current, a first line conductive to said low frequency current, and means for connecting` said low frequency thereto, a' second line circuit substantially non-conductive to said lowl frequency current, a secondary Winding on said transformer connected to said second line circuit under control of said means and path for applying said loW frequency current to said first mentioned transformer Winding to modulate said high frequency carrier current in accordance with said low frequency.

7. ln a signaling system, a first vand a second line section, a source of high frequency current to said first mentioned trans;A prising a short circuiting Vibrator, a source of direct current and a primary Winding for a transformer, a source of low frequency curr-ent for said second line section, a control means for energizing said second line section from the source of low frequency current, means for modulating said high frequency current by said low frequency current and means affected by said contr l means forr energizing said first line section from said modulated high frequency current.

8. ln a signaling system, a transformer, current sources to provide energy at a first and a second frequency for energizing Windinffs of said transformer and effecting modulation of said first frequency by said second frequency, selective paths to eect separation of said frequencies relative to the respective sources, and means for employing said modulated current and current at said secondary frequency in sigualinG.

9. Ina signaling system, sources of high and loW frequency current, a transformer energizedby said currents for effecting modulation of said high frequency current by said low frequency current, a plurality of selective paths for isolating current of one source from the sources of the other frequencies, andrmeans for applying said modulated current and unmodulated currents in signaling. i

ln Witness whereof, l hereunto subscribe my name this 1st day of Gctober, A. D. 1924i.

HENRY l/V. ONEILL. 

